Children of divorced parents are usually dependents of the custodial
parent. There are exceptions. The custodial parent can release the
exemption to his or her ex-spouse by signing a written declaration (Form 8332)
that the noncustodial spouse must attach to the tax return each year he
or she claims the children as dependents. Or if your divorce decree
gives your ex-spouse the right to claim the children, he can do so if he
attaches key pages of that document to his tax return. Otherwise, you
get to claim the children as your dependents. If your ex-spouse claims
them, too, the IRS will step in and likely deny his claim. Also read What Happens When Both Parents Claim a Child on a Tax Return for more information on this topic.